This invention relates to fluid swivels for an offshore hydrocarbon production or transfer system.
Fluid swivels are commonly used to pass oil, natural gas and other fluids between an undersea well or pipeline, and a weathervaning ship. Such a fluid swivel commonly includes inner and outer main parts, where one part can rotate about a vertical axis without limit relative to the other part as the ship weathervanes. The main swivel parts form an annular transfer chamber between them through which fluid passes, with upper and lower gap passages extending from the transfer chamber to the environment, and with seals along the gap passages.
Fluid passing through the fluid swivel often contains some sand, which can settle out of the fluid and which tends to migrate into the lower gap passage. Such sand is highly abrasive, and tends to greatly reduce the life of seals located along the lower gap passage. A fluid swivel which minimized the migration of sand into the lower gap passage, would increase the life of seals lying along the lower gap passage.